In WHMCS, go to Setup > Addon Modules and activate the module, making sure you grant access to your role.

Enter your License Key and Company ID provided in your welcome email into the relevant fields.

Go to Addons > Xero in WHMCS and click the link to download your public key. If a key isn't provided, follow these instructions and upload the generated private and public key to the `modules/addons/xero` folder.